Object production

ABSTRACT

Methods and apparatus for producing an object, the method comprising: performing an Additive Manufacturing process to produce an intermediate object from provided metal or alloy, whereby the intermediate object comprises regions having a contaminant concentration level above a threshold level; based upon one or more parameters, determining a temperature and a duration; and performing, on the intermediate object, a contaminant dispersion process by, for a duration that is greater than or equal to the determined duration, heating the intermediate object to a temperature that is greater than or equal to the determined temperature and less than the melting point of the metal or alloy, the contaminant dispersion process being performed so as to disperse, within the intermediate object, a contaminant from regions of high contaminant concentration to regions of low contaminant concentration until the intermediate object comprises no regions having a contaminant concentration level above the threshold level.

CROSS-REFERENCE TO RELATED APPLICATION

This application is the National Stage of International Application No.PCT/GB2013/050410, filed 20 Feb. 2013, which claims the benefit of andpriority to GB 1203359.3, filed 24 Feb. 2012, and GB1301173.9, filed 23Jan. 2013, the contents of all of which are incorporated by reference asif fully set forth herein.

FIELD OF THE INVENTION

The present invention relates to the production of objects.

BACKGROUND

Additive Manufacturing (AM) (also known as Additive Layer Manufacturing(ALM), 3D printing, etc.) refers to processes that may be used toproduce functional, complex objects, layer by layer, without moulds ordies. Typically, AM processes include providing material (e.g. metal,ceramic or plastic) in the form of a powder or a wire, and, using apowerful heat source (such as a laser beam, electron beam or anelectric, or plasma welding arc), an amount of that material is meltedand deposited upon a base work piece. Subsequent layers are then builtup upon each preceding layer so as to form the object.

Example AM processes include, but are not limited to, Laser BlownPowder, Laser Powder Bed, and Wire and Arc technologies.

However, objects produced using AM processes, particularly those madeusing powder material, may comprise one or more contaminated regions,i.e. regions in which the material that forms the object has beencontaminated by a contaminant (e.g. oxygen). Also, objects producedusing AM processes, particularly those made using powder material, maycomprise micro-pores and other imperfections at or proximate to thesurface of the object. The presence of such contaminated regions andother imperfections tend to adversely affect the fatigue performance ofan object, especially in high-cycle fatigue situations. For example, theimperfections may act as crack initiators.

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides a method of producingan object, the method comprising: providing some metal or alloy;performing, using an Additive Manufacturing apparatus, an AdditiveManufacturing process to produce an intermediate object from theprovided metal or alloy, whereby the intermediate object comprises oneor more regions having a contaminant concentration level above athreshold level; based upon one or more parameters selected from thegroup of parameters consisting of: the type of metal or alloy from whichthe intermediate object has been produced, the shape and/or size of theintermediate object, a contaminant concentration level of a region ofthe intermediate object, and the threshold level, determining atemperature and a duration; and performing, on the intermediate object,a contaminant dispersion process by, for a duration that is greater thanor equal to the determined duration, heating the intermediate object toa temperature that is greater than or equal to the determinedtemperature and less than the melting point of the metal or alloy fromwhich the intermediate object has been made, the contaminant dispersionprocess being performed so as to disperse a contaminant from regions ofhigh contaminant concentration within the intermediate object to regionsof low contaminant concentration within the intermediate object untilthe intermediate object comprises no regions having a contaminantconcentration level above the threshold level, thereby producing theobject.

The contaminant dispersion process may be performed such that thecontaminant is substantially uniformly distributed within the bulk ofthe object.

The contaminant dispersion process may comprise performing, on theintermediate object, a hot isostatic pressing process at a temperaturethat is greater than or equal to the threshold temperature and for aduration that is greater than or equal to the threshold duration.

The determined temperature may be between 1100° C. and the melting pointof the provided metal or alloy.

The determined temperature may be between 1300° C. and the melting pointof the provided metal or alloy.

The determined duration may be greater than or equal to one hour.

The determined duration may be greater than or equal to two hours.

The Additive Manufacturing (AM) process may be a process selected fromthe group of AM processes consisting of: a powder bed fusion AM process,a blown powder AM process, a sheet lamination AM process, a laser blownpowder AM process, a laser powder bed AM process, and an AM process thatimplements wire and arc technology.

The metal or alloy from which the object is made may be selected from agroup of metals or alloys consisting of: titanium alloys, steel, nickelsuperalloys and aluminium alloys.

The metal or alloy may be Ti-6Al-4V.

The metal or alloy may be provided in powder form.

The Additive Manufacturing process may be a powder bed AdditiveManufacturing process.

The contaminant may comprise oxygen.

The intermediate object may comprise a plurality of open cavities. Themethod may further comprise performing a sealing process on theintermediate object to seal the openings of the open cavities, therebyforming a plurality of closed cavities, and reducing the sizes of theclosed cavities by performing a consolidation process on theintermediate object having the closed cavities.

The produced object may comprise a plurality of open cavities. Themethod may further comprise performing a sealing process on the objectto seal the openings of the open cavities, thereby forming a pluralityof closed cavities, and reducing the sizes of the closed cavities byperforming a consolidation process on the object having the closedcavities.

The step of reducing the sizes of the closed cavities may be performedat least until the closed cavities are no longer present.

The step of performing a consolidation process may comprise performing ahot isostatic pressing process.

The step of performing a sealing process may comprise plasticallydeforming the surface of the object.

Plastically deforming the surface of the object may comprise shotpeening the surface of the object.

The step of performing a sealing process may further comprise sinteringthe object after the surface of the object has been plasticallydeformed.

The method may further comprise determining a contaminant concentrationlevel of a region of the intermediate object.

The determined temperature and duration may be based upon the determinedcontaminant concentration level.

The determining of a contaminant concentration level of a region of theintermediate object may comprise determining the maximum contaminantconcentration level within the intermediate object.

In a further aspect, the present invention provides a method ofproducing an object, the method comprising: providing an initial object,the initial object being made of a metal or an alloy, the initial objecthaving been produced by performing an Additive Manufacturing process,the initial object comprising one or more regions having a contaminantconcentration above a threshold level; based upon one or more parametersselected from the group of parameters consisting of: the type of metalor alloy from which the initial object has been produced, the shapeand/or size of the initial object, a concentration level of a region ofthe initial object, and the threshold level, determining a temperatureand a duration; and performing, on the initial object, a contaminantdispersion process by, for a duration that is greater than or equal tothe determined duration, heating the initial object to a temperaturethat is greater than or equal to the determined temperature and lessthan the melting point of the metal or alloy from which the initialobject has been made, the contaminant dispersion process being performedso as to disperse a contaminant from regions of high contaminantconcentration within the initial object to regions of low contaminantconcentration within the initial object until the initial objectcomprises no regions having a contaminant concentration above thethreshold level, thereby producing the object.

In a further aspect, the present invention provides an object that hasbeen produced using a method according to any of the above aspects.

In a further aspect, the present invention provides apparatus forproducing an object, the apparatus comprising: Additive Manufacturing(AM) apparatus configured to, using some provided metal or alloy,perform an Additive Manufacturing process to produce an intermediateobject from the provided metal or alloy, whereby the intermediate objectcomprises one or more regions having a contaminant concentration levelabove a threshold level; means for, based upon one or more parametersselected from the group of parameters consisting of: the type of metalor alloy (12) from which the intermediate object has been produced, theshape and/or size of the intermediate object, a contaminantconcentration level of a region of the intermediate object, and thethreshold level, determine a temperature and a duration; and heatingmeans configured to perform, on the intermediate object, a contaminantdispersion process by, for a duration that is greater than or equal tothe determined duration, heating the intermediate object to atemperature that is greater than or equal to the determined temperatureand less than the melting point of the metal or alloy from which theintermediate object has been made, the contaminant dispersion processbeing performed so as to disperse a contaminant from regions of highcontaminant concentration within the intermediate object to regions oflow contaminant concentration within the intermediate object until theintermediate object comprises no regions having a contaminantconcentration level above the threshold level, thereby producing theobject.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration (not to scale) showing exampleAdditive Manufacturing apparatus;

FIG. 2 is a process flow chart of an embodiment of a process ofproducing an object;

FIG. 3 is a schematic illustration (not to scale) showing a stage of anAdditive Manufacturing process performed by the Additive Manufacturingapparatus; and

FIG. 4 is a schematic illustration (not to scale) of a cross section ofthe object at a certain stage of the process of FIG. 2.

DETAILED DESCRIPTION

FIG. 1 is a schematic illustration (not to scale) showing exampleAdditive Manufacturing apparatus 2 that is to be used, in an embodiment,to perform an Additive Manufacturing process so as to create an object4.

The terminology “Additive Manufacturing” is used herein to refer to alladditive processes that may be used to produce functional, complexobjects, layer by layer, without moulds or dies e.g. by providingmaterial (e.g. metal or plastic) in the form of a powder or a wire, and,using a powerful heat source such as a laser beam, electron beam or anelectric, or plasma welding arc, melting an amount of that material anddepositing the melted material (e.g. on a base plate/work piece 6), andsubsequently building layers of material upon each preceding layer.

Additive Manufacture (AM) may also be known inter alia as 3D printing,Direct Digital Manufacturing (DDM), Digital Manufacturing (DM), AdditiveLayer Manufacturing (ALM), Rapid Manufacturing (RM), Laser EngineeringNet Shaping (LENS), Direct Metal Deposition, Direct Manufacturing,Electron Beam Melting, Laser Melting, Freeform Fabrication, LaserCladding, Direct Metal Laser Sintering.

In this embodiment, the AM apparatus 2 is apparatus for performing apowder bed AM processes. Further information on powder bed AM apparatusand processes may be found, for example in Gibson, I. Rosen, D. W. andStucker, B. (2010) “Additive Manufacturing Technologies: RapidPrototyping Direct Digital Manufacturing” New York, Heidelberg,Dordrecht, London: Springer, which is included herein by reference.However, in other embodiments, a different type of AM apparatus is usedproduce the object 4, e.g. by performing a different type of AM process.Examples of other appropriate AM processes that may be used to producethe object 4 include, but are not limited, blown powder AM processes,sheet lamination AM processes, vat photopolymerisation AM processes,laser blown powder AM processes, laser powder bed AM processes, and AMprocesses that implement wire and arc technology.

In this embodiment, the AM apparatus 2 comprises a heat source in theform of a laser source 8 configured to produce a high powered laser beam10. The laser source 8 may be any appropriate type of laser source, e.g.a laser source that is configured to have a continuous wave power outputof 500 W.

The AM apparatus 2 further comprises a source of metallic material(hereinafter referred to as “metallic powder 12) in the form of a powderrepository 14 (or powder bed). In this embodiment, the metallic materialis titanium alloy powder (e.g. Ti-6Al-4V). Titanium alloy powdertypically has spherical grains with a diameter in the range 0-45 μm.

In other embodiments, a different type of material (e.g. a differenttype of metallic power, a plastic powder, or a ceramic powder) may beused.

In operation, a first piston 16 (that is located at the bottom of thefirst repository) is raised (in the direction indicated by an arrow inFIG. 1 and the reference numeral 18) so as to raise an amount of thepowder 12 above a top level of the repository 14.

In this embodiment, a roller 20 is rolled (in the direction indicated byan arrow in FIG. 1 and the reference numeral 22) over the upper surfaceof the repository 14 and across an upper surface of a further repository24. This is performed so that the metallic powder 12 that was raisedabove the level of the repository 14 by the raising of the first piston16 is spread over an upper surface of the further repository 24. Thus, atop surface of the contents of the further repository 24 is covered by alayer of metallic power 12. In other embodiments, a different means ofspreading the metallic powder 12 across a top surface of the contents ofthe further repository 24, such as a wiper, may be used instead of or inaddition to the roller 20.

After a layer of metallic power 12 has been spread across a top surfaceof the contents of the further repository 24, the laser source 8 iscontrolled by a computer 26 to deliver the laser beam 10 via an opticalfibre 28 to focussing optics 30 which focus the laser beam 10 to thefocal point 32 on the layer of metallic power 12 has been spread acrossa top surface of the contents of the further repository 24.

The laser beam 10 produced by the laser source 8 is focused upon thelayer of metallic powder 12 has been spread across the top surface ofthe contents of the further repository 24 so as to melt a portion of thelayer of metallic powder 12.

In this embodiment, a portion of the metallic powder 12 on the topsurface of the further repository 24 is fully melted, and subsequentlyallowed to cool so as to form a layer of solid material.

A second piston 34, located at the bottom of the further repository 24is then lowered (i.e. moved in a direction indicated in FIG. 1 by asolid arrow and the reference numeral 36) to allow for a further layerof metallic powder 12 to be spread by the roller 20 (and subsequentlymelted and allowed to solidify) across the top surface of the contentsof the further repository 24.

Many layers of material are laid on top of one another (in accordancewith a digital design model 38 for the object 4 stored by the computer26) to produce the object 4.

In this embodiment, the laser source 8 and focussing optics 30 aremoveable under the control of the computer 26 in an X-Y plane that isparallel to the top surface of the contents of the further repository 24(i.e. a top surface of the object 4). Thus, the laser focal point 14 maybe directed to any point in a working envelope in the X-Y plane so thatlayers of material of a desired shape may be deposited.

Thus, AM apparatus 2 for performing a process of producing, inaccordance with an embodiment, the object 4 is provided.

FIG. 2 is a process flow chart of an embodiment of a process ofproducing (i.e. manufacturing, building, constructing, etc.) the object4 using the above described example AM apparatus 2.

The object 4 that is to be produced by the method of FIG. 2 may be anyappropriate type of object having any appropriate size and shape. Inthis embodiment, the produced object 4 is made of titanium or a titaniumalloy. However, in other embodiments, the produced object 4 is made of adifferent material to the object 2 in this embodiment.

At step s2, a three dimensional digital model 38 of the object 4 (thatis to be produced) is provided. The digital model 38 of the object 4 isa digital design model for the object 4.

In this embodiment, the digital model 38 is stored by the computer 26.In this embodiment, the digital model 38 can be viewed, manipulated andanalysed using the computer 26 e.g. by implementing a suitable softwarepackage or tool.

At step s4, a base plate is provided. The base plate provides a parentstructure upon which layers of material are to be added (by the AMapparatus 2 performing the AM process) so as to form the object 4. Inthis embodiment, the base plate may, for example, be secured to thesecond piston 34 e.g. using any appropriate means.

At step s6, the AM apparatus is calibrated. This calibration processmay, for example, include accurately measuring the base plate 6 and/orproviding or creating a three dimensional digital model of the baseplate 6. These data and the digital model 38 of the object 4 may be usedto generate a “tool path” that, during the AM process, will be followedby the AM apparatus 2 so as to produce the object 4.

At step s8, using the AM apparatus 2, an AM process is performed to addlayers of material to the base plate 6, and thereby form the object 4.In this embodiment, the AM apparatus 2 is for performing a powder bed AMprocess and is described in more detail above with reference to FIG. 1.In this embodiment, the AM process is the powder bed AM processdescribed in more detail above with reference to FIG. 1. Furtherinformation on powder bed AM apparatus and the powder bed AM process canbe found, for example in the above mentioned “Additive ManufacturingTechnologies: Rapid Prototyping Direct Digital Manufacturing”, which isincorporated herein by reference. However, in other embodiments, adifferent type of AM apparatus and/or process is used produce the object4.

In this embodiment, the AM process is performed in a substantially inertatmosphere (e.g. a chamber that is back-filled with an inert gas e.g.argon).

In this embodiment, the AM process comprises using a laser beam 10 tomelt metallic powder 12 at the laser focal point 14. Typically, as thisis performed, small droplets of molten material, or powder grains thathave been heated by the laser beam 10, are ejected or sprayed (e.g. bythe forces created by the heating process) away from the focal point 14of the laser beam 10.

FIG. 3 is a schematic illustration (not to scale) showing small dropletsof molten material (hereinafter referred to as the “droplets” andindicated in FIG. 3 by the reference numeral 40) being ejected, expelledor sprayed away from the focal point 14 of the laser beam 10 during theAM process. In some embodiments, instead of or in addition to liquiddroplets 40 of molten material being ejected, expelled or sprayed awayfrom the focal point 14 of the laser beam 10 during the AM process,heated solid particles of metallic material may be ejected and may alsobecome contaminated by gasses or vapours present in the chamberatmosphere.

In this embodiment, the droplets 40 (and solid heated particles) havebeen heated by the laser beam 10. Due to their elevated temperature andhigh surface area relative to their volume, the droplets 40 (and solidheated particles) tend to be highly reactive. Thus, the droplets 40 (andsolid heated particles) tend to react with any contaminants that arepresent in the chamber atmosphere 42 in which the AM process is beingperformed. For example, the droplets 40 may absorb oxygen gas that hascontaminated the chamber atmosphere 42 and is present in the chamber inwhich the AM process is being performed. Also for example, the droplets40 may react with any water vapour that has contaminated the chamberatmosphere 34 and is present in the chamber in which the AM process isbeing performed.

In this embodiment, a proportion of the droplets 40 (and solid heatedparticles), that have reacted with the contaminant within the chamberatmosphere 42 and that have been sprayed, or expelled away from thelaser focal point 14, land on the surface of the object 4 being formed.Such a droplet 40 (or solid heated particle) of contaminated materialmay be “welded” into the structure of the object 4 when the laser beam10 is focused at the location on the surface at which that contaminatedmaterial landed.

Also in this embodiment, a proportion of the droplets 40, that havereacted with the contaminant within the chamber atmosphere 42 and thathave been sprayed, or expelled away from the laser focal point 14, landin a bed of un-melted titanium powder 12 contained within the furtherrepository 24 and surrounding the object 4 being formed. The unusedmetallic powder 12 contained within the further repository 24 isrecycled (i.e., reused in the AM process that is performed to producethe object 4, or in future AM processes). Thus, recycled powder that hasabsorbed a contaminant may be bonded, or welded, into the structure ofthe object 4.

Thus, the object 4 produced using the AM process of step s8 may compriseone or more contaminated regions. In other words, the object 4 maycomprise regions in which the material of the object 4 is contaminated(by a contaminant such as oxygen).

At step s10, after the object 4 has been produced by the AM process, theobject 4 is allowed to cool and, in this embodiment, the object 4 isremoved from the further repository 24. Excess (i.e. unused or unmelted)metallic power 12 may be removed from the object, e.g. using an air jet,or by washing the object.

Thus, the object 4 is formed. The remaining steps of the process of FIG.2 describe the processing of the object 4 formed at step s10 that isperformed, in this embodiment to produce the finished object 4.

FIG. 4 is a schematic illustration (not to scale) of a cross section ofa portion of the object 4 produced by performing steps s2 to s10 asdescribed above.

The surface 44 of the object 4 is relatively uneven, i.e. rough.

In this embodiment, proximate to its surface 44, the object 4 comprisesa plurality of open cavities 46 (i.e. open pores or voids in thematerial body). These open cavities 46 are cavities or hollows that areopen to the atmosphere, i.e. cavities or hollows that are connected tothe surface 44 of the object 4 such that gas can flow from outside theobject 4 into the those open cavities 46.

Also, the object 4 further comprises a plurality of closed cavities 48(i.e. closed pores or voids in the material body). These closed cavities48 are hollow spaces or pits in the body of the object 4. Furthermore,the closed cavities 48 are not open to the atmosphere, i.e. they are notconnected to the surface 44. In other words, gas cannot flow fromoutside the object 8 into the closed cavities 48 and vice versa.

Also, the object 4 further comprises a plurality of contaminated regions50 (i.e. regions in which material that has previously absorbed orreacted with a contaminant, such as oxygen, has been incorporated, i.e.bonded or welded). In some embodiments, a contaminated regions 50 may bethe result of the titanium powder raw material being contaminated e.g.by an undesired metal such as tungsten, copper or iron or a ceramicmaterial such as an oxide, nitride or carbide. The contaminated regions50 within the object may have a different chemical structure to thematerial that forms the rest of the object matrix (i.e. to theuncontaminated titanium object 4). Also, the contaminated regions 50within the object 4 may have different material properties (e.g. theymay be harder, or softer, and may cause degradation of fatigueperformance) than the material that forms the rest of the object matrix(i.e. to the uncontaminated titanium object 4).

The presence of micro-pores (i.e. the open and closed cavities 46, 48)and the other imperfections (i.e. the contaminated regions 50) in theobject 4 tend to adversely affect the fatigue performance of the object4, especially in high-cycle fatigue situations. For example, thecavities 46, 48 and contaminated regions 50 may act as crack initiators.Also, the cavities 46, 48 and the contaminated regions 50 tend toadversely affect the load-bearing characteristics of the object 4.

In conventional methods, after the object 4 has been formed at step s8,the object may be further processed so as to smooth the rough surface44. For example, a machining or polishing process may be performed.However, such processes tend to be inappropriate when attempting tofully remove the open cavities 46. Furthermore, such processes tend notto shrink, or remove, the closed cavities 48 or the contaminated regions50 from the object 4. Machining the surface 44 of the object 4 to asufficient depth may be performed to remove surface roughness andcavities connected to the surface 44. Machining may expose internalclosed cavities that were originally isolated and machining tends to berelatively expensive and, depending on the complexity of the shape ofthe object 4, would at least partly negate the cost advantage of using anet-shape-process to form the object 4. Polishing processes also removematerial from an object and so, if continued to a sufficient depth, maybe performed to remove surface roughness and surface connected cavities.Polishing processes also tend to be relatively expensive to perform.Also, processes such as Hot Isostatic Pressing (HIPing), that may beemployed to remove internal pores, tend not to have any effect onsurface connected cavities.

Deficiencies of conventional methods of producing objects/parts may beovercome by performing steps s12 to s16 on the object 4, as opposed tojust performing a machining/polishing process. Thus, the object formedat step s10 may be thought of as an “intermediate object” that is to befurther processed (in accordance with steps s12 to s16) to produce a“final object”.

At step s12, the object 4 produced at step s10 is peened.

A conventional shot peening process may be used. For example, a processin which the surface 44 of the object 4 is impacting with shot (e.g.substantially round particles made of metal, glass or ceramic) withsufficient force such that the object 4 is plastically deformed at itssurface 44 may be implemented. Also for example, laser, or ultra-sonic,peening may be performed.

In embodiments in which the surface 44 of the object 4 is impacted withshot, any appropriate shot medium may be used, e.g. S330 (cast steelwith an average diameter of 0.8 mm). Also, any appropriate shot peeningpressure may be used, e.g. 0.5 bar, 0.75 bar, 1.25 bar, 2 bar and 4 bar.Also, any appropriate Almen intensities may be used, e.g. 0.15 mmA, 0.20mmA, 0.30 mmA, 0.38 mmA and 0.52 mmA.

After peening, the surface 44 of the peened object is relatively smooth(compared to the surface 44 prior to peening).

Furthermore, the process of shot peening tends to plastically deform theobject 4 at its surface 44 such that the openings of the open cavities46 are either closed such that gas cannot flow from outside the object 4into an open cavity 46 and vice versa (i.e. such that, in effect, anopen cavity 46 becomes a closed cavity 48), or are closed such that theopening of an open cavity 46 to the surface 44 is very small but thatgas may still flow from outside the object 4 into an open cavity 46 andvice versa.

In this embodiment, the plastic deformation of the surface 44 of theobject 4 is performed by peening. However, in other embodiments adifferent plastic deformation process is used, for example, a process ofburnishing e.g. using a roller. Such finishing methods (e.g. tumbling,burnishing, shot peening etc.) tend not to remove material from anobject.

At step s14, the peened object 4 is sintered.

In this embodiment, a temperature at which, and duration for which, theobject is sintered is selected or determined.

The value for the sintering temperature is determined based upon anyappropriate parameters, such that, when the object is heated to or abovethat temperature, contaminant is diffused within the object 4 (fromregion having high contaminant concentration to regions having lowcontaminant concentration) at or above a desired rate.

The value for the sintering duration is determined based upon anyappropriate parameters, such that, when the object is heated to or abovethe determined sintering temperature for that duration, the maximumcontaminant concentration level within the object 4 is below a thresholdvalue. In some embodiments, the sintering duration is determined suchthat, when the object is heated to or above the determined sinteringtemperature for that duration, the contaminant concentration levelwithin the object 4 is substantially uniform.

Examples of appropriate parameters that may be used to determine thesintering temperature or duration include, but are not limited to, thetype of metal or alloy from which the object has been produced, theshape and/or size of the object, a contaminant concentration level of aregion of the object (e.g. a maximum contaminant concentration levelwithin the object 4), and a threshold contaminant concentration levelbelow which the maximum contaminant concentration level within theobject 4 is to be reduced.

In this embodiment, the object 4 is sintered at relatively hightemperate. For example, the sintering of the peened object may comprisesintering at a temperature in the range 900° C. to the melting point ofthe object. In this embodiment, the object 4 is made of Ti-6Al-4V, themelting point of which is approximately 1600° C. Preferably, the object4 is sintered at or above a temperature of 1100° C. More preferably, theobject is sintered at or above a temperature of 1300° C.

In this embodiment, the object is sintered for a relatively long periodof time, e.g. 1 hour, or 2 hours, or longer. The length of timesintering is to be performed for may depend upon the type of materialfrom which the object 4 is made, or any other appropriate parameter.

In this embodiment, the sintering process is performed for a timeperiod, and at a temperature, that provide the following:

-   -   the openings of the open cavities 46 (that were either closed or        almost closed by the peening process of step s10) are diffusion        bonded such that, in effect, the open cavities 46 become closed        cavities 48. In other words, the openings of the open cavities        46 are fully sealed by sintering the object 4;    -   the contaminant(s) within the contaminated regions 50 of the        object 4 are diffused within the object 4, e.g. throughout the        bulk of the object. Preferably, this is performed such that the        contaminant is dispersed substantially uniformly throughout the        bulk of the object 4, i.e. such that no one region of the object        4 has a substantially higher concentration of contaminant than a        different region of the object 4.

In this embodiment, the peened object 4 is sintered at a temperaturethat is below the melting point of the material from which the object 4is made.

One advantage of plastically deforming the surface prior to sintering isthat recrystallisation and diffusion bonding during high temperaturesintering tends to be faster and more effective at smoothing the surfaceand closing open cavities when compared to an undeformed surface. Thismay, for example, be due to stored dislocation energy and residualstress within the object 4.

At step s16, a hot isostatic pressing (HIP) process is performed on thesintered object 4.

A conventional HIP process is used to reduce the porosity, and increasethe density, of the sintered object 4. In this embodiment, the sinteredobject 4 is subjected to elevated temperature and elevated isostatic gaspressure by subjecting the sintered object 4 to heated and pressurisedargon. A HIP cycle having a duration of approximately 2 hours, atemperature of 920° C., and a pressure of 102 MPa may be used.

The HIP process produces a relatively high pressure at the surface 44 ofthe sintered object 4, whilst the pressures in the closed cavities 48(including the open cavities 46 that have been formed into closedcavities 48 as described above) are relatively low. This is due to theclosed cavities 48 not being open to the surface 44, i.e. beinggas-tight. As a result of plastic deformation, creep, and/or diffusionbonding caused by the elevated temperature and pressure, the closedcavities 48 in the sintered object 4 shrink or vanish completely.

The HIP process performed on the sintered object may cause diffusion ofthe contaminants within the objects 4. However, at a typical HIPtemperature of 920° C., in titanium, the diffusion rates of mostcontaminants e.g. oxygen, nitrogen, carbon, etc. tend to be relativelylow and sufficient to disperse contamination over only small distances,e.g. a few microns. In contrast, at a typical sintering temperature of1300° C., the diffusion rate of contaminants tends to be several ordersof magnitude faster than it is at 920° C., and therefore diffusiondistances are correspondingly much greater. The sintering processdescribed above may be thought of as a “contaminant homogenisationprocess”, i.e. a process of homogenising a concentration of acontaminant within an object produced using an AM process.

The hot isostatic pressing of the sintered object 4 produces thefinished object 4. Thus, a process of producing the object 4 isprovided.

In the above embodiments, the process of producing the object comprisespeening, sintering and subsequently HIPing an object. This process ofpeening, sintering and subsequently HIPing an object may be performed inaccordance with any of the methods described in patent applicationGB1203359.3, “Processing of Metal or Alloy Objects”, filed at the UnitedKingdom Intellectual Property Office (UKIPO) on 24 Feb. 2012, andincorporated herein, in its entirety, by reference.

An advantage provided by the above described methods is that pores,pits, or other (e.g. minute) openings, orifices, or interstices in thesurface of the object tend to be removed. In other words, defects and/ordiscontinuities at or proximate to the surface of the object may, ineffect, be repaired. These open cavities may act as crack initiators.Thus, removal of these open cavities from the object tends to result inimproved fatigue performance, especially in high-cycle fatiguesituations. The improved surface finish and microstructure of the objecttend to improve its fatigue performance.

The above described methods also tend to remove (or shrink) the closedcavities (or other voids or hollows that are closed to the surface) inthe body of the object. This also tends to improve the microstructure ofthe object, which tends to lead to improved fatigue performance.

A further advantage provided by the above described methods is thatregions with relatively high concentrations of contaminants within anobject produced using an AM process tends to be removed. Regions withrelatively high levels or concentrations of a contaminant within anobject (i.e. the contaminated regions 50) tend to have differentmaterial properties than the material that forms the rest of the objectmatrix, and may act as crack initiators or adversely affect theproperties of the object. Thus, removal of these relatively contaminatedregions (i.e. by more evenly distributing the contaminant throughout theobject 4) tends to result in improved fatigue performance and materialproperties of the object 4.

Conventionally, objects produced using AM processes are not typicallytreated by sintering those objects at high temperatures. This is partlyfor cost reasons and partly because high temperature sintering of suchan object tends to increase the grain size within the object, therebyreducing the strength of the object. However, the present inventors haverealised that, surprisingly, the benefits gained by sintering the objectso as to more evenly (e.g. uniformly) distribute contaminants within theobject outweigh the disadvantages of performing the sintering process(i.e. the increased grain size).

Objects produced using an above described process tend to be able towithstand a greater maximum stress, and/or withstand a greater number offatigue load cycles to failure, when compared to objects produced usinga conventional AM process.

A further advantage provided by the above described methods is that thesurface finish of the object tends to be improved. The object tends tobe smoother and shinier than those that are produced using conventionaltechniques. This increased reflectivity is important in certainapplications. For example, if the object is for decorative purposes, theimproved aesthetic appearance of the object tends to be important. Alsofor example, the object tends to be less likely to retain dirt orsurface contamination, and be easier to clean and less abrasive.

A further advantage provided by the above described processes is that anobject is produced by an AM process. This tends to provide that theobject is produced with very little wastage. Furthermore, it tends to berelatively easy to make relatively complex shapes that may beprohibitively expensive to machine.

The above described processes are advantageously applicable to objectsof any size. The treatment process (e.g. a process of shot peening,sintering, and hot isostatic pressing) is performed after the formationof the object (i.e. after the performance of the AM process).

A further advantage provided by the above described processes is thatthe some of them may be performed on a large number of objectssimultaneously. Thus, a cost of performing any or all of theseoperations (per component) may be significantly reduced.

A further advantage provided by the above described method is that ametallic powder that is known to contain contaminants may be used, byperforming an AM process, to create an object that has substantially thesame or better material/fatigue properties as a different object thathas been produced, using the same AM process, from a metallic powderthat contains fewer impurities or contaminants. This is because theobject created from the relatively more contaminated powder may betreated (using the treatment processes described herein) so as toimprove the material/fatigue properties of the object to be the same orbetter than those of the object formed from the relatively lesscontaminated powder. Thus, costs of producing an object having givenmaterial/fatigue properties may be reduced.

It should be noted that certain of the process steps depicted in theflowcharts of FIG. 2 and described above may be omitted or such processsteps may be performed in differing order to that presented above andshown in FIG. 2. Furthermore, although all the process steps have, forconvenience and ease of understanding, been depicted as discretetemporally-sequential steps, nevertheless some of the process steps mayin fact be performed simultaneously or at least overlapping to someextent temporally.

Apparatus, including the computer, may be provided by configuring oradapting any suitable apparatus, for example one or more computers orother processing apparatus or processors, and/or providing additionalmodules. The apparatus may comprise a computer, a network of computers,or one or more processors, for implementing instructions and using data,including instructions and data in the form of a computer program orplurality of computer programs stored in or on a machine readablestorage medium such as computer memory, a computer disk, ROM, PROM etc.,or any combination of these or other storage media.

In the above embodiments, the object is formed using a powder bed AMprocess. However, in other embodiments the object is formed using adifferent type of AM process, for example, a blown powder process, asheet lamination process, a vat photo-polymerisation process, a LaserPowder Bed process, or an ALM process that implements Wire and Arctechnologies.

In other embodiments, the treatment process performed on the objectproduced using an AM process comprises peening, sintering, and hotisostatic pressing.

However, in other embodiments, the treatment process comprises thesintering process, and not the peening or HIPing processes. The hightemperature sintering process advantageously tends to provide that thecontaminant(s) within the contaminated regions of the object diffusewithin the object, e.g. throughout the bulk of the object e.g. such thatno one region of the object has a substantially higher concentration ofcontaminant than a different region of the object. This advantageouslytends to result in improved fatigue performance and material propertiesof the object.

Also, in other embodiments, the treatment process comprises the hotisostatic pressing process, and not the sintering or peening processes.The hot isostatic pressing process advantageously tends to provide thatthe closed cavities in the object shrink or vanish completely. Thisadvantageously tends to result in improved fatigue performance andmaterial properties of the object. Also, if performed at a suitably hightemperature (i.e. >900° C.), and for a suitably long duration, the hotisostatic pressing process advantageously tends to provide that thecontaminant(s) within the contaminated regions of the object diffusewithin the object, e.g. throughout the bulk of the object e.g. such thatno one region of the object has a substantially higher concentration ofcontaminant than a different region of the object. This advantageouslytends to result in improved fatigue performance and material propertiesof the object.

In some embodiments, the peening process is omitted.

In the above embodiments, the object is formed from a titanium alloy(e.g. an alloy comprising titanium with 6% aluminium and 4% vanadiumwhich is also known as Ti-6Al-4V, or 6-4, 6/4, ASTM B348 Grade 5).However, in other embodiments, the object is formed from a differentmaterial. For example, in other embodiments, the object is formed from apure (i.e. unalloyed) metal or a different type of alloy to that used inthe above embodiments, or a ceramic.

In the above embodiments, the treatment process (i.e. a process ofpeening, sintering, and hot isostatic pressing) is performed on a singleobject. However, in other embodiments, a treatment process, or part of atreatment process, may be performed on any number of (different or thesame) objects. This advantageously tends to reduce the cost of theprocess per component.

In the above embodiments, the sintering of the object is performed atthe above specified temperatures, and for the above specifiedtime-periods. However, in other embodiments sintering of an object isperformed at a different appropriate temperature and/or for a differentappropriate time period.

In the above embodiments, the HIP process is performed at the abovespecified temperatures and pressures, and for the above specifiedtime-periods. However, in other embodiments a HIP process is performedat a different appropriate temperature and/or pressure, and/or for adifferent appropriate time period.

In the above embodiments, the sealing process performed on the object toseal the openings of the open cavities (i.e. the process of shot peeningand sintering, or the process of coating and heating) is performed oncebefore the HIP process is performed on the object. However, in otherembodiments, before the HIP process is performed, one or both of thesealing processes may be performed multiple times. For example, thesealing process of peening and sintering may be performed more thanonce. In such an example, the sintering process that follows a shotpeening process, tends to soften the work hardened surface formed duringshot peening and tends to disperse any surface contamination into thebulk of the object, making the surface of the object more amenable toanother shot peening process. Furthermore, the second, and anysubsequent, shot peening processes may be performed at a lower intensitythan the first shot peening process. This tends to result in a bettersurface appearance.

1. A method of producing an object, the method comprising: providingsome metal or alloy; performing, using an Additive Manufacturingapparatus, in an environment containing an amount of a reactivecontaminant, an Additive Manufacturing process to produce anintermediate object from the provided metal or alloy, wherein theAdditive Manufacturing processes includes heating the provided metal oralloy thereby causing at least some of the metal or alloy to react withthe reactive contaminant in the environment so as to producecontaminated metal or alloy, the intermediate object comprises thecontaminated metal or alloy, and the intermediate object comprises oneor more regions in which concentration level of the contaminated metalor alloy is above a threshold level; based upon the threshold level anda concentration level of the contaminated metal or alloy within one ormore of the regions, determining a temperature and a duration; andsintering the intermediate object for a duration that is greater than orequal to the determined duration at a temperature that is greater thanor equal to the determined temperature and less than the melting pointof the metal or alloy so as to disperse the contaminated metal or alloyfrom the regions to one or more further regions within the intermediateobject having a lower concentration level of the contaminated metal oralloy until the intermediate object comprises no regions having aconcentration level of the contaminated metal or alloy above thethreshold level, thereby producing the object.
 2. A method according toclaim 1, wherein the sintering is performed such that the contaminatedmetal or alloy is substantially uniformly distributed within the bulk ofthe object.
 3. A method according to claim 1, wherein the method furthercomprises, after the sintering process, performing, on the intermediateobject, a hot isostatic pressing process.
 4. (canceled)
 5. A methodaccording to claim 1, wherein the determined temperature is between1300° C. and the melting point of the provided metal or alloy.
 6. Amethod according to claim 1, wherein the determined duration is greaterthan or equal to one hour. 7-9. (canceled)
 10. A method according toclaim 1, wherein the metal or alloy is Ti-6Al-4V.
 11. A method accordingto claim 1 wherein, the metal or alloy is provided in powder form andthe Additive Manufacturing process is a powder bed AdditiveManufacturing process.
 12. A method according to claim 1, wherein thereactive contaminant is oxygen.
 13. A method according to claim 1,wherein the intermediate object comprises a plurality of open cavities,and the method further comprises: performing a sealing process on theintermediate object to seal the openings of the open cavities, therebyforming a plurality of closed cavities; and reducing the sizes of theclosed cavities by performing a consolidation process on theintermediate object having the closed cavities.
 14. A method accordingto claim 1, wherein the produced object comprises a plurality of opencavities, and the method further comprises: performing a sealing processon the object to seal the openings of the open cavities, thereby forminga plurality of closed cavities; and reducing the sizes of the closedcavities by performing a consolidation process on the object having theclosed cavities.
 15. A method according to claim 13, wherein the step ofreducing the sizes of the closed cavities is performed until the closedcavities are no longer present.
 16. A method according to claim 13,wherein the step of performing a consolidation process comprisesperforming a hot isostatic pressing process.
 17. A method according toclaim 13, wherein the step of performing a sealing process comprisesplastically deforming the surface of the object.
 18. A method accordingto claim 17, wherein plastically deforming the surface of the objectcomprises shot peening the surface of the object.
 19. A method accordingto claim 17, wherein the step of performing a sealing process furthercomprises sintering the object after the surface of the object has beenplastically deformed.
 20. A method according to claim 1, wherein: themethod further comprises determining a concentration level of thecontaminated metal or alloy within a region of the intermediate object;and the determined temperature and duration are determined using thedetermined contaminant concentration level.
 21. A method according toclaim 20, wherein the determining of a concentration level of thecontaminated metal or alloy within a region of the intermediate objectcomprises determining the maximum concentration level of thecontaminated metal or alloy within the intermediate object. 22.(canceled)
 23. Apparatus for producing an object, the apparatuscomprising: Additive Manufacturing apparatus configured to, using someprovided metal or alloy, in an environment containing an amount of areactive contaminant, perform an Additive Manufacturing process toproduce an intermediate object from the provided metal or alloy, whereinthe Additive Manufacturing process include heating the provided metal oralloy thereby causing at least some of the metal or alloy to react withthe reactive contaminant in the environment so as to produce acontaminated metal or alloy, and the intermediate object comprises oneor more regions in which a concentration level of the contaminated metalor alloy is above a threshold level; means for, based upon the thresholdlevel and the concentration level of the contaminated metal or alloywithin one or more of the regions, determine a temperature and aduration; and sintering means configured to sinter the intermediateobject for a duration that is greater than or equal to the determinedduration at a temperature that is greater than or equal to thedetermined temperature and less than the melting point of the metal oralloy so as to disperse the contaminated metal or alloy from the regionsto one or more further regions within the intermediate object having alower concentration level of the contaminated metal or alloy until theintermediate object comprises no regions having a concentration level ofthe contaminated metal or alloy above the threshold level, therebyproducing the object.
 24. An object that has been produced using amethod according to claim
 1. 25-26. (canceled)
 27. A method according toclaim 1, wherein the step of performing comprises: performing, using theAdditive Manufacturing apparatus, in the environment containing anamount of the reactive contaminant, an initial Additive Manufacturingprocess, the initial Additive Manufacturing processes including heatingthe provided metal or alloy, thereby causing at least some of the metalor alloy to react with the reactive contaminant in the environment so asto produce the contaminated metal or alloy; and performing, using theAdditive Manufacturing apparatus, a further Additive Manufacturingprocess, to produce the intermediate object from metal or alloy recycledfrom the initial Additive Manufacturing process, the metal or alloyrecycled from the initial Additive Manufacturing process including thecontaminated metal or alloy.